Creating an allow-then-deny MQTT filter with MyQtthub

Then deny rest of topics PUBLISHed to all users (or optionall to some users).

Go to filters clicking top menu:

…and then Filters:

Now click to add filter (top right):

Now input a label, select a high priority (higher than deny rule; 1 has higher priority than 100), select rule type (limit PUBLISH), leave rule enabled and configure topic filters that are going to be allowed: